The flyash particleboard was a kind of composite material with the flyash as the main material and the wood flake as the reinforcement through hot pressing. The adhesive mechanism of flyash particleboard was discussed and analysed from the physical and chemical properties, activity and hydration mechanism of flyash; action mechanism of temperature and additive agent as well as the microstructure analyses from scanning electron microscope （SEM） and X ray diffractometer （XRD）. It was concluded that the adhesive mechanism of the flyash particleboard was a multi active and complex physicochemical process.